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QCA7e_ch02_szb_handouts

QCA7e_ch02_szb_handouts - Daniel C Harris Quantitative...

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1 Quantitative Chemical Analysis Seventh Edition Quantitative Chemical Analysis Seventh Edition Chapter 2 Tools of the Trade Daniel C. Harris Daniel C. Harris Topics in this chapter Basic laboratory apparatus and manipulations – Safety – Notebook – Mass: Balance – Volume: Burets, Vol. Flasks, Pipets, Syringes – Filtration – Drying – Calibration – Spreadsheets
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2 The smallest scales
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3 Safety • Eye protection - goggles • Close heel and toe shoes • Avoid bare legs and arms – lab coat • Use gloves when appropriate • Wash gloved hands before removing gloves • Use fume hood • Label all vessels to indicate what they contain • Dispose of waste properly
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4 • Write clearly • Setup notebook for numerical data before lab • Show ALL calculations and include units • Record complete file spec for all computer files • You may want to have sections on: – The purpose - Write chemical equations – The methods used – Results (experimental data) – Conclusions • Most important: – be able to reproduce from your notes Lab Notebook The analytical balance Displacement of the balance pan generates a correction current. The electromagnet then restores the pan to its initial position. N and S are the north and south poles of the permanent magnet.
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5 Calibration of the Balance • Analytical balances calibrate themselves automatically with a standard mass on the load-bearing structure • Less expensive electronic balances are calibrated at the factory – gravity may not be the same as the force of gravity in your lab • Periodically check your balance by weighing a standard mass. Balance weights
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6 Buoyancy Buoyancy is the upward force exerted on an object in a liquid or gaseous fluid. An object weighed in air appears lighter than its actual mass by an amount equal to the mass of air that it displaces. Buoyancy error occurs when the density of the object being weighed is not equal to the density of the standard mass. Buoyancy Correction If mass m ’ is read from a balance, the true mass m of the object weighed in vacuum is given by: d a is the density of air (0.0012 g/mL near 1 bar and 25 ° C) d w is the density of the calibration weights (typically 8.0 g/mL) d is the density of the object being weighed
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7 Example Buoyancy Correction Calculation A pure compound called “tris” is used as a primary standard to measure concentrations of acids. The volume of acid required to react with a known mass of tris tells us the concentration of the acid. Find the
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